An aerostatic bearing is a key component of a precision moving table, which provides the moving table with gas bearing support and thereby enables a friction-free movement thereof on a platform (which is generally a marble platform). Typically, an aerostatic bearing includes air floating elements and a vacuum pre-tightening structure.
FIG. 1 shows a square aerostatic bearing of the prior art, in which air floating elements 2a, 2b, 2c, 2d are disposed respectively at four corners of a bottom of an aerostatic bearing plate 1 and a vacuum pre-tightening structure 3 is disposed at a center portion of the aerostatic bearing plate 1. Both the air floating elements 2a, 2b, 2c, 2d and the vacuum pre-tightening structure 3 are formed integrally from the aerostatic bearing plate 1.
As shown in FIG. 2, during the operation of the square aerostatic bearing, positive pressure gas is introduced into the air floating elements 2a, 2b, 2c, 2d to form a gas membrane between the aerostatic bearing and the platform 4, thereby enabling the aerostatic bearing to be supported by an aerostatic force N and thus enabling the aerostatic bearing to move frictionlessly on the platform 4. Meanwhile, negative pressure gas is introduced into the vacuum pre-tightening structure 3 to generate a vacuum pre-tightening force F operated on the aerostatic bearing in an opposite direction to the aerostatic force N. Adjusting the aerostatic force N and the vacuum pre-tightening force F can change the aerostatic stiffness of the aerostatic bearing.
Above described is an integral-type aerostatic bearing whose air floating elements and vacuum pre-tightening structure are integrally formed from a single aerostatic bearing plate. Such aerostatic bearing is characterized in that the increase of its aerostatic stiffness requires the increase of both the aerostatic force N and the vacuum pre-tightening force F at the same time. However, the increase of the vacuum pre-tightening force F will lead to a bending of a central portion of the aerostatic bearing plate 1 (as shown by the dotted lines in FIG. 2). As the thickness δ of the gas membrane is generally only several micrometers to a dozen or more micrometers, when the bending amount σ of the aerostatic bearing plate 1 is large, the central portion of the aerostatic bearing plate 1 may contact with the platform 4, and hence generate mechanical friction which can disable the floating effect of the aerostatic bearing.